Embodiments of the present invention relate to microelectromechanical systems (MEMS) devices. More particularly, embodiments of the present invention relate to packaged MEMS devices attached to a printed circuit board (PCB).
MEMS devices are widely employed in electrical and electronic systems to perform a variety of tasks. MEMS devices often include small mechanical structures, and thus the devices are generally enclosed in a protective package in order to be reliably utilized in a system. The package includes electrical connectors, such as leads, pins, balls, or lands, attached to the external surface of the package that offer communication between the MEMS device and the system. Typically, installation in a system involves mounting the package on a PCB such that the electrical connectors of the package contact electrically conductive pads or holes on the PCB. The package connectors are typically coupled to the PCB conductors with solder, a flowable usually metallic material.
While the primary purpose for using solder to couple package connectors to PCB conductors is to provide a highly-reliable, low-resistance electrical connection between the connectors and the conductors, solder also provides a relatively strong mechanical connection between the connectors and the conductors, and in turn, the MEMS device package and the PCB. With a strong mechanical connection between the package and the PCB, mechanical stresses and deformations of the PCB can be transferred to the MEMS device package. Similarly, thermal stresses on the PCB may also be transferred to the MEMS device package. Overall, MEMS devices are sensitive to package stress. MEMS devices enclosed in non-hermetic plastic packages are particularly sensitive to mechanical stress. For example, MEMS devices that provide measurements, such as accelerometers or pressure sensors, may provide erroneous readings when under stress. To correct these errors, frequent calibration must be performed or compensation algorithms may have to be employed. Furthermore, it is possible that the accuracy of MEMS accelerometers may suffer even after the stress on the package is removed. Therefore, traditional techniques to implement a packaged MEMS device on a PCB may lead to poor performance of the MEMS device that requires calibration or compensation techniques or results in degraded system performance.